Police are trying to determine if a substance passed among four first-graders in a city school Friday was cocaine.

One of the youngsters at Charles Carroll of Carrollton Elementary School brought nine vials of a powdery white substance to school and shared the contents of two of the vials with three classmates while they worked on a group project Friday afternoon.

Two of the vials were empty when their teacher, Dorothy Polk-Bostic, took them away from the children, said Robyn Washington, city schools' spokeswoman.

The school nurse who examined the children and school police suspected the vials contained cocaine, called the children's parents and recommended hospital treatment for the children.

"Was this an illegal substance? We don't know," said Harold Eason, Carroll's principal. "But because we had children who ingested something, we acted immediately."

Three of the youngsters were treated at Johns Hopkins Hospital and released, and school officials encouraged the father of the fourth student to have him examined.

"As far as we know, they are OK," Mr. Eason said yesterday.

The three girls and one boy were working in a group when their teacher noticed them passing around something that was not included in the project, said Ms. Washington. She took the vials and two of the girls to the principal and the nurse. Later, it was determined that the two other youngsters also had tasted the substance.

"Obviously, these children thought they had what we used to call 'pixie sticks,' " straws of flavored granular candy that children shake into their hands or directly down their throats, Ms. Washington said.

The girl who brought the vials to school at first said they were part of her Nintendo game and later said that they belonged to the boyfriend of a relative, Ms. Washington said. School officials contacted the child's family and determined that she is in the custody of her grandmother.

Ms. Washington said it was unclear whether the child thought the vials contained candy or had any idea they might contain an illegal substance.

School police turned over the evidence to city police for testing.

Johns Hopkins spokesman Michael Purdy would not disclose the results of cocaine tests performed on the youngsters treated at the hospital, but said those results would be turned over to police.